Abstract In psychology and basic medical science, many studies have been performed with experiments on animals such as rats and mice, to clarify mechanisms of mental disorders. With this aim, several mental disorder model rats and mice have been developed by genetic manipulation, giving psychotropic drugs, injuring their brain or breeding under special conditions. Social interaction test is one of the experimental protocols to evaluate their appropriateness. However, this test is not popular because of lack of reproducibility. Thus, we consider the robotic agent that interacts with a rat/mouse in the social interaction test provides new opportunities to perform it under more strict conditions. We have then developed a quadruped animaroid, WR-1. WR-1 has four 3-DOF legs, 2-DOF waist and 1-DOF neck. WR-1 walks with both crawl and trot gait. WR-1 also reproduces rearing and head shake behavior. Size of WR-1 is larger and motion performance lower than those of a mature rat. However, in a social interaction test with a rat and WR-1, some social interactions were observed between them.

Key words; Quadruped robot, Social interaction test of rats, Behavioral robotics

I. INTRODUCTION In basic medical science and psychology, many studies

have been performed with experiments on animals such as rats and mice, to clarify mechanisms of mental disorders such as depression, anxiety disorders and schizophrenia. In these studies, mental disorder model rats/mice have been developed by genetic manipulation, giving psychotropic drugs, injuring their brain or breeding under special conditions [1][2][3]. The appropriateness of them has been evaluated through behavior tests such as the social interaction test, the open-field test, the forced swimming test and the fear

Hiroyuki ISHII, Ph. D., Research associate of Waseda University 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo, Japan h-ishii@takanishi.mech.waseda.ac.jp www.takanishi.mech.waseda.ac.jp

conditioning test. With this methodology, mechanisms of the mental disorders have been clarified progressively. For instance, Hiroi founded out one of the casual factors in schizophrenia via the experiments using 22q11.2 (a part of the chromosome) overexpression mice [1]. Many experiments on animals also have been performed to develop new drugs for the mental disorders. In these experiments, the new drugs were given to the disorder model rats/mice and effectiveness and safety of these drugs were evaluated through the behavior tests [4][5][6].

Concerning the mental disorders of humans, social interaction is key issue. However, several researchers consider social interactions between animals dont have enough reproducibility, hence social interaction is not well considered in the experiments on animals. We consider a robotic agent that interacts with animals provides new opportunities to perform the social interaction tests under more strict conditions. We have then developed a quadruped animaroid as a robotic agent in the social interaction tests.

Up to now, several quadruped robots inspired from quadruped animals have been developed. One of the most famous quadruped robots is AIBO [7]. This robot is developed for home entertainment. Big Dog and Little Dog are also one of them. Big Dog is developed as a transport machine and Little Dog is developed for research on learning locomotion [8][9]. Therefore, these robots are not designed to

Development of Quadruped Animaroid for Social Interaction Test with Rats and Mice

H. Ishii*, A. Komura**, Y. Masuda**, S. Miyagishima**, A. Takanishi***,

S. Okabayashi****, N. Iida****, H. Kimura**** *Institute for Biomedical Engineering, Waseda University

**Graduate School of Science and Engineering, Waseda University ***Faculty of Science and Engineering, Waseda University

****Faculty of Letters, Arts and Science, Waseda University

Fig. 1 Rat-like quadruped robot WR-1 and rat

2009 IEEE/ASME International Conference on Advanced Intelligent MechatronicsSuntec Convention and Exhibition CenterSingapore, July 14-17, 2009

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be used in the interaction experiments with real animals. We also developed two quadruped robots. The first one has four 2-DOF legs. The size and weight is almost equal to a mature rat [10]. However, this robot doesnt reproduce rats social behavior such as rearing, sniffing or mounting. The second one also has four 2-DOF legs, and it has 1-DOF waist yaw joint [11]. However, this robot doesnt reproduce rats social behavior either. Thus, we developed a new quadruped animaroid that interacts with a rat.

In this paper, we describe the quadruped animaroid WR-1.

II. SOCIAL INTERACTION TEST OF RATS

A. Outline of the Test The social interaction test was developed to provide an

ethologically based test that was sensitive to both anxiolytic and anxiogenic effects [12]. It is sensitive to a number of environmental and physiological factors that can affect anxiety. It has detected anxiogenic effects of peptides such as corticotropin-releasing factor (CRF) and adrenocorticotropic hormone (ACTH), and anxiolytic effects of neuropeptide Y and substance P receptor antagonists.

B. Experimental Protocol In this test, two rats are put into a circle or square

open-field together. Experimental duration of this test is less than 10 minutes. During these 10 minutes, the numbers of the interactions such as mounting, wrestling, biting, chasing, sniffing, licking and social grooming are measured by observation.

Like other behavior test, two groups with different conditions, control group and experimental group, are prepared. The subjects in the experimental group are manipulated to make abnormal emotional state by genetic manipulation, giving psychotropic drugs or breeding under special conditions while those in the control group are not.

C. Problem Some researchers mentioned lack of reproducibility of the

social interaction test. The social interactions between animals are not reproducible at all. Thus, the result of the social interaction test changes depending on several factors that are not able to be controlled.

III. ANALYSIS OF RATS BODY STRUCTURE AND MOTION Before designing the new quadruped animaroid, we

analyzed body structure of a rat. An X-ray picture of rats skeleton is shown in figure 2. Referring to this picture and anatomy charts of a rat [13], we designed a DOF arrangement model of a rat as shown in figure 3. In this model, each leg consists of 3 DOF, a shoulder pitch, a shoulder roll and an elbow/knee pitch, and the waist consists of 2 DOF, a pitch and yaw. This model also has a pitch at the neck. The body proportion of a rat was also obtained by analyzing the X-ray picture.

Gait analysis was done using the box with a transparent

floor. Sequential photographs taken from under the floor are shown in figure 4. According to analysis on these pictures, we confirmed that rats ran with trot gait while they walked with crawl gait.

IV. DESIGN OF RAT-LIKE QUADRUPED ROBOT, WR-1 Based on the analysis described in chapter III, we designed

the new quadruped animaroid, WR-1 (Waseda Rat No.1) as

Fig. 4 Analysis on rats walking, black circle represent support leg and white circle represent swing leg

Fig. 3 DOF arrangement model of rats

Fig. 2 X-ray picture of a rat, a skeleton and its proportion of each part to the spine are shown.

0.28 1

0.2

0.24

0.2

0.2

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shown in figure 5 and 6. Each joint is actuated by a small servo motor unit as shown in table 1. To make WR-1 have same proportion of a mature rat (see figure 2), its legs must be quite small and slim comparing to its body. Therefore, the elbow pitch joints and the knee pitch joints are actuated by the motors that are implemented in the body via timing belts as shown in figure 7.

To keep the center of gravity at the back side of the body, a battery and a control circuit are implemented at the hip. WR-1 is covered with a white fur with yellow and blue plates for image processing.

V. CONTROL OF WR-1

A. Walking Pattern Generator We developed a dynamic walking pattern generator for

WR-1 based on the theory of ZMP stability criterion [14][15]. Kinematic model with mass distribution as shown in figure 8 (b) is implemented in this generator. It computes time-line data of each joint angle based on the procedure as shown below;

1) Selecting gait (crawl / trot) 2) Making target trajectory of each foot 3) Making initial trajectory of the body 4) Making target ZMP trajectory 5) Computing compensation motion of the body using the

repeated computation as shown in figure 8 (a).

Neck pitch

Shoulder pitchElbow pitch Hip pitch

Knee pitch

Waist pitchWaist yaw

Hip rollShoulder roll

Fig. 5 Design of WR-1

Table 1 Specification of the actuators implemented in WR-1 Elbow pitch/ Knee pitch/

Shoulder pitch/ Hip pitchShoulder roll/

Hip roll/ Waist yaw Waist pitch Neck pitch

Model (manufacturer)

S3102 (Futaba servo)

DSR3801 (JR PROPO)

KRS-786ICS (Kondo Kagaku)

Waypoint W-068(Air craft)

Size mm 28 x 13 x 30 26 x 15 x 33 35 x 21 x 41 22 x 10 x 23 Weight g 21 30 45 6.2 Speed sec/60deg 0.25 0.11 0.17 0.10 Torque Nm 0.36 0.70 0.85 0.09

Fig. 6 Photograph of WR-1

xx yy

zz

270270130130

110

110

Fig. 7 Design of front leg

xy

z

Motor for drivingelbow pitch

Motor for drivingshoulder pitch

Elbowpitch

Shoulderpitch

Timing belt

Timing belt

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B. Onboard controller WR-1 has the onboard controller that consists of a

microcontroller (dsPIC 30H3013) and a wireless communication module. All the servo motors are controlled by this controller. 9 motion patterns, as shown in table 2, are implemented in the microcontroller as time-line data of each joint angle. The motion pattern of number 2, 3, 4, 5 and 6 are beforehand computed using the walking pattern generator. The microcontroller generates control signals to the servo motors based on the pattern when it receives the instruction (number of motion in table 2) from the PC via the wireless communication module.

Table 2 Motion patterns implemented in WR-1

Number Motion 1 Stop 2 Walk forward (crawl) 3 Run forward (trot) 4 Walk back 5 Turn right 6 Turn left 8 Rear 9 Shake head

C. Behavior control system using visual feedback control The social interaction tests using a rat and WR-1 are

performed in an open-field (see figure 12). Behavior of WR-1 is controlled by the PC using visual feedback control as shown in figure 9. The control software that is implemented in the PC consists of three software modules, the image processing module, the operation generator module and robot controller module. Behavior of WR-1 is determined by the operation generator module. The operation generator module has two different operation modes, one is an automatic interaction mode and the other is a manual operation mode. With the automatic following mode, the software controls the robot to follow the rat and to rear once a minute. With the manual operation mode, a human operator controls the robot motion via the keyboard inputting the motion number like radio control toys.

VI. EVALUATION OF WR-1

A. Motion Performance Motion performance of WR-1 obtained from validation

test is shown in figure 10 and table 3. The maximum running speed is 0.03 m/s. Sequential pictures of walking are shown in figure 11 (a) and those of rearing are shown in figure 11 (b). Comparing to a mature rat, WR-1 is a little bit larger and motion speed is a little bit slower.

Computing inertial force generated by motion of legs

Computing body trajectory to make ZMP trajectory on target

ZMP trajectory

Computing motion of each leg using inverse kinematics

Computing ZMP

eM isacceptable?

Motion pattern of each joint is obtained.

Start

Computing error moment eM

(a) Algorithm of computing walking pattern

(b) Kinematics model with mass distribution of WR-1 Fig. 8 dynamic walking pattern generator for WR-1

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Table 3 Motion performance of WR-1 Dimension mm 130270 110 Weight g 1150 Speed (straight) m/s 0.03 Speed (rotation) rad/s 0.06

Gait Crawl Trot

Behavior Rearing Head shake

B. Social Interaction with Rat We performed a social interaction test with a rat and WR-1.

The test is done with the experimental protocol as shown below.

1) WR-1 and a rat are put into the open-field (700 x 700) together.

2) WR-1 keeps following a rat and rear once a minute. 3) WR-1 rears once a minute. 4) Behavior of the rat is observed. 5) Experimental duration is 10 minutes.

In this test, some kind of social interactions such as chasing, rearing, sniffing and licking were observed as shown in figure 12 and 13. However, more active social interactions, such as mounting, biting or wrestling were not observed.

VII. CONCLUSION We developed a new quadruped animaroid WR-1 that

reproduces social behavior of a rat such as sniffing or rearing. This robot was designed referring to anatomic charts of a rat and analysis on rats skeleton and walking. WR-1 has four 3 DOF legs, 2-DOF waist and 1-DOF neck. The size and weight are a little bit larger than those of a mature rat.

0

5

10

15

20

25

30

0 10 20 30

Wal

king

spe

ed m

/s

Step mm

x10-3

zTrotzCrawl

Fig. 10 Walking performance of WR-1

WR-1 Rat

Open fieldInstructiondata

Image Processing

Operation Generator

Control PC

Bluetooth

CCD camera

Robot Controller

Interaction

Fig. 9 Automatic robot control system

1 2 3

4 5 6

(a) Trot walking

1 2 3

4 5 6

(b) Rearing Fig. 11 Actual motion of WR-1

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However, in the social interaction test with a rat, some social interactions, sniffing and grooming are observed.

To realize smoother and more real social interaction with a rat, the quadruped animaroid needs to be more small and high performance. We are going to develop more small and high performance robot.

ACKNOWLEDGMENT A part of this study was conducted at the Humanoid

Research Institute (HRI), Waseda University. We also would like to express our thanks to Solid Works Corp., Advanced Research Institute for Science and Engineering of Waseda University.

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confers antipsychotic-responsive be-havioral abnormalities in mice, Proceedings of the National Academy of Science of U.S.A., 102(52), 19132-7, 2005.

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[3] M. N. Hill, et al., Regional alterations in the endocannabinoid system in an animal model of depression: effects of concurrent antidepressant treatment, Journal of Neurochemistry, Vol. 106, 2008.

[4] C. LinksLouis, et al., Additional evidence for anxiolytic- and antidepressant-like activities of saredutant (SR48968), an antagonist at the neurokinin-2 receptor in various rodent-models, pharmacology, biochemistry and behavior, Vol. 89 (1), pp. 36-45, 2008.

[5] K.R. Starr, SB-649915-B, a novel 5-HT1A/B autoreceptor antagonist and serotonin reuptake inhibitor, is anxiolytic and displays fast onset activity in the rat high light social interaction test, Neuropsychopharmacology, Vol. 32(10), pp.2163-72, 2007.

[6] G. Bagdy, et al., Anxiety-like effects induced by acute fluoxetine, sertraline or m-CPP treatment are reversed by pretreatment with the 5-HT2C receptor antagonist SB-242084 but not the 5-HT1A receptor antagonist WAY-100635, 1: International Journal of Neuropsychopharmacol, Vol. 4(4), pp. 399-408, 2001.

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[13] F.W. Warren, G. H. Dominique, Anatomy and Dissection of the Rat, W. H. Freeman, 1997.

[14] H. Nishizawa, A. Takanishi., H. Lin, Realization of Quadruped Walk with ZMP stable, Proceedings of RSJ2003, 2003.

[15] A. Takanishi, J. Yamaguchi, M. Iwata, Dynamic Quadruped Walking Stabilized with Trunk Motion, Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems 1995, 1995.

a b

c

Fig. 12 Social interaction test with WR-1 and a Rat; a) Chasing, b) Sniffing, c) Rearing of WR-1.

Fig. 13 Social interaction test with WR-1 and a Rat, side view

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